The invention refers to a pressure relief apparatus at a supporting element beam for metal strand casting plants, particularly for curved steel strand casting plants, which is set for the strand vein width essentially by means of connecting rods, spacer pieces, and arrestable adjustment devices arranged next to the strand cross section, or which may be set for the distance matching the desired strand thickness between opposed supporting elements and tightened at the supporting element frame.
Such supporting element beams require exact adjustment to the respective strand shape, and simultaneously require simple resetting procedures for altered strand thickness. The distance set between two respective supporting elements (which consist, in the area of the casting strand leaving the strand casting molds, of sheet-like bodies, and in the remaining areas, of rollers or of a number of rollers assembled on an axis) must ensure absolute guidance for the casting strand which still has liquid in the interior.
It is known to arrange cylinders with cooperating helical surfaces, such as grooved spindles with cooperating threaded nuts, in the axis of the connecting rods to fulfill the requirement of easy adjustment of the supporting rollers. The angle of inclination of the helical surfaces must be smaller than the pertaining or built-in friction at rest. The slide cylinders may be synchronously driven by means of hydraulic cylinders according to German Pat. No. 26 12 094 in order to adjust the supporting roller distance. This arrangement requires self-checking or built-in friction of the helical slide surfaces according to the thread pitch of a threaded spindle. Such self-checking is disadvantageous in those cases where the casting strand solidifies irregularly, and exerts increased forces onto the supporting rollers when traversing the supporting roller stand. The forces occurring then cannot be predetermined mathematically with sufficient accuracy. With basic unanticipated forces it is, therefore, not inconceivable that the relief apparatus is blocked at the moment when it should be operating.
Another disadvantage results from the extreme case when the casting strand further cools at a standstill in the supporting roller stand due to interruption of the casting process and finally completely solidifies and exerts further expansion forces onto the supporting rollers. This case is especially applicable to curved metal strand casting plants. The expansion forces increase the friction on the slide surfaces of the spacer cylinders. The adjustment of the spacer cylinders then requires, accordingly, large drives, thus not only causing greater expenditures, but also a considerable space requirement.
Another problem with current technology is the basic choice of a hydraulic or purely mechanical drive to position the supporting element beams towards the strand vein, and/or to adjust the strand thickness, and/or to adjust the distance between opposite supporting elements. Another disadvantage in current technology for hydraulically operating means of adjustment is that self-checking spacing spindles, for example, may be released by a breakdown of hydraulic pressure in the piston-cylinder units. The application of a spacing cylinder with a built-in check thus requires a hydraulic adjusting drive for the supporting element beams. This means that it is not possible to use a self-checking spacing cylinder when using mechanical means of adjustment, such as traction spindles with threaded nuts. It has been found that the increase in clamping force caused by return forces of the casting strand onto the supporting elements, leads to an increase in the self-checking thread forces, so that movement of the threaded nut on the threaded spindle is prevented.
Based on this, the present invention relates to a relief apparatus without the above-mentioned shortcomings, i.e. requiring less expenditures and less space and which, at the same time, functions safely and is particularly suitable for support element beams which are adjusted to the strand vein by means of arrestable mechanical adjusting elements.
According to the invention, within the power flow going through the connecting rod, a switch-on, switch-off power link is provided with which to detach at least one supporting element beam of a supporting element beam pair from its bracing support by switching off the power link. Such power link may be incorporated within the connecting rod/threaded spindle/threaded nut arrangement in such a way that it will not require any additional space. The power link according to the invention is also safer in operation, as it is structured on the existing clamping force of the cast strand. That is, it depends on the magnitude of the clamping force. In principle, the power link permits the application of a relief apparatus with supporting element beams which are equipped with mechanical means of adjustment.
Following the basic idea of the invention, a short-stroke piston-cylinder unit with a valve blocking the discharge of pressure medium is arranged as a switch-on, switch-off power link between the supporting element beams and supporting element frames braced by means of supports and/or threaded spindles and threaded nuts. The concept of the invention requires merely a minimum volume filled with pressure medium, leaving a clearance of about 30 mm which suffices to transport the cast strand without difficulty away from between two opposed supporting elements.
Another space-saving feature results from the threaded nut existing in mechanical adjusting drives which the present invention uses, in that the switch-on, switch-off power link is arranged within the threaded nut of a threaded spindle/threaded nut arrangement transmitting the arresting force, such power link consisting of an annular cylinder with annular piston. In the sense of the compact construction of the power link it is, furthermore, advantageous if a viscous material, such as grease, is used as pressure medium in the piston-cylinder unit.
The operation of the power link, according to the invention, includes the outlet lock valve arranged outside the cooling chamber of the strand casting plant and connected with the piston-cylinder unit via a pressure line. The outlet lock valve may be set for a certain pressure, so that the relief apparatus is automatically started when this pressure is exceeded. On the other hand, the outlet lock valve may also be controlled manually and its effective range altered in accordance with the cooling status of a particular cast strand.
In very difficult cases, e.g. with curved metal strand casting plants with a great curvature, a greater relief of the supporting element beam, i.e. greater application of the supporting rollers, may be desired than that which is achieved by means of the power link and its short stroke. In that case, the invention includes an additional measure where, between the threaded nut and the supporting element frame, a rotatable spacer cylinder surrounding the shaft of the threaded nut is arranged, supported on the annular piston and the supporting element frame, whereby the spacer cylinder is axially displaceable in one peripheral position only. After activating the power link, and turning the spacer cylinder into the indicated peripheral position, the respective supporting element beam may, without any difficulty, be removed from the counter supporting element by means of a crane, hydraulic plunger, or similar device, to a desired opening position with the desired spacing.
The distance between the opposed supporting elements and/or the opposed supporting element beams is maintained by inserting U-shaped adapters at the supporting element frame between an annular collar or extension on the threaded spindle, and a contact surface.